Impulse generator



Dec. 26, 1939. K. SCHLESINGER IMPULSE GENERATOR Filed July 23, 1936 2 Sheets-Sheet 1 imam ax?" 1939- K. SCHLESINGER 2,185,131

IMPULSE GENERATOR Filed July 25, 1936 ZSheets-Sheet 2 IMPULSE GENERATOR Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignmentato Loewe Radio, Inc., a corporation of New York Application July 23, 1936, Serial-No. 92,154l

In Germany July 29, 1935 3 Claims.

The invention relates to methods and apparatus for generating very exact synchronisation impulses from sinusoidal and filtered control frequencies; these frequencies being equal to those of the impulses or to a multiple of. them, and the duration of the impulses being capable of being adjusted to be as short as desired. The apparatus generates simultaneously two groups of impulses, short line and long frame synchronisation impulses. It is ensured by special measures in accordance with the invention that there exists a mutual dependency of these two groups of impulses so that a frame signal can onlyini-- tiate at once with a line signal or,.in the case 16 of certain methods, exactly. in the middle between two line signals that is to say with the precision which is defined by the initiation of a line signal.

In this way there is avoided the fluctuation of terfering in television.

The invention is illustrated in the accompanying drawings in which- Fig. 1 shows the diagram of a single impulse generator, a

Fig. 2 is an oscillogram, whilst I Fig. 3 shows the diagram of a complete generator arrangement for line and frame impulses.

As basic element for generating the impulses there is employed a reversal of the known relaxation generator, the discharge tube being used for charging the storage condenser, which has already been described and employed in itself in an earlier application (U. S. application No. 24,902, filed June 4, 1935). There is charged the condenser I in Fig. 1, when the tube 2 is ignited by a control impulse, by an anode battery 3 of approximately 50-100 volts. Its control grid has a strong negative bias 4 of approximately volts, so that an ignition of thetube can only take place when there arrive by way of the line 5 positive potential peaks which raise the grid above the ignition value. "A strong grid current is prevented in the known fashion (see U. S.'application No. 668,940, filed May 2, 1933) by means of the current limiting resistance 6. After the ignition the tube is traversed by a powerful charging current until the storage condenser I has its full positive charge.

The charging itself, owing to the low inner resistance of the tube and if the condenser l is not too large, takes place extremely quickly, so that there may be obtained at l a positive impulse with steep front. The charging current is limited by a resistance 31, which is large incomparison with the inner resistance of the tube 2 The discharge of condenser I takes place through a resistance It.

the linesin the image frequently found to bein- In the oscillogram, Fig. 2, there are shown two wavelengths of a sinusoidal control tone frequency. The grid bias of the tube is entered in the same diagram in the form of a broken line 12. The first ignition accordingly takes place at 5 the point l3. There immediately commences the charging period, which is completed upon expiry of the time 1-=R1-C (R1=inner resistance of the ignited tube, C=capacity of 1:). Upon expiry of this period the impulse potentiol I l in the upper 10 diagram in Fig. 2 has reached .the value of the anode potential 3.1 The tube is extinguished at the point I 5. If the leak resistance I0 were so small that the discharge were to take place according to the curve [6, i. e., that the same were 15 completed before arrival of the second control tone change. a new ignition would occur at the point IT. The number of impulses per second would accordingly be equal to the control frequency. If in accordance 'with the invention the 20 duration of the discharge RIOC! is made considerably longer, 1. e., the resistance Ill increased in size, so that the discharge occurs according to Ilia, the second control-impulse is unable to effect ignition at I! because the bias between grid. and cathode is still too negative, and the next ignition occurs at the point l8, i. e., omitting one control-impulse. In the case of a fixed time constant RIO'CI according to curve Ilia, Fig. 2, an impulse generation may be enforced at each 3 single control impulse by increasing the amplitude of the latter. In accordance with the invention'the control impulses are made variable in intensityby means of a potentiometer 26, Fig. 1 (see also the bottom of Fig. 3), so that at this '85 potentiometer the sequence of impulses may be adjusted as 1: /2:%, etc. "To the discharge circuit 9, ill an amplifying tube I9 is coupled by way of condenser 20, a grid leak resistance 2| and a grid current limiting reso sistance 22. This protective resistance ensures that too high positive potentials of the grid of I9 are avoided. It should amount to 1 to 1 megohm being large in relation to the leak it. By reason of its use there are obtained impulses 4;; having a rectangular top.

In a television receiver two connection systems of this kind are provided. The line-impulse connection operates with 1= 30O cm., 10:13

- megohm,.whilst the frame-change connection op- 50 limiters 22a: and 223 on an appertaining amplifying tube I91: and I911. The two anodes are connected via a. common anode resistance 23 to a variable anode potential source'24 so that the impulse amplitudes of both groups are equal and adjustable. In order to avoid any reaction between amplifi I and generators there are employed as poweramplifiers 19 screening grid tubes, preferably pentodes. For each screening grid and the appertaining generator a separate apparatus Na: and Ny is provided.

Now it will be described-how the y-side of the.

and a condenser 29 (1 mi.) At' the potentiometer 26 there are adjusted the number of frame changes per image according to the remarks made in conjunction with Fig. 2. The mains frequency is now first freed by means of a filter chain 30/3I of all harmonic vibrations (0.1 megohm, 0.1 mf.) The control frequency generator 45 is represented in practice by an amplifier, which is connected with a photo-cell arranged behind a rim of slots in the scanning disc 32 chopping the light of the lamp 43. The disc 32 is driven by a mains-fed synchronous motor (not shown).

It is possible by using a highly selective amplie fier having-a plurality of tuned circuits tosobtain a very precise control frequency which'is independent of irregularities of the slot divisioning in the disc 32. This signal may be 'equal to the frequency or to the octave of this frequency, in the latter case the apparatus Ta: having the task of halving the frequency. By means of a by-pass consisting of the condenser 33 (approximately .001 mf.), the resistance 34 (approximately 0.1 megohm) an adjustable fraction of this control energy may be applied, in addition to the mains frequency, to the grid of Ty in order to secure synchronisation.

In the interlaced line-group system the octave of the line frequency is supplied by 45. In this case the octave of the line frequency, and not the line frequency itself, is likewise employed for synchronisation by way of the passage 33 /34. The

line frequency itself is produced only in Ta: and

must be carefully withheld from the by-pass. For this purpose the series resistance 36 is provided. The operation of Ty by both frequencies has the desired effect of fixing the impulse initiation for the frame-change signals once at the commencement of the line and again at the middle of the line, as necessary in the case of the interlaced line method.

It may be specifically pointed out that in the above there have been described merely particular forms of embodiment of the general idea according to the invention, and that the stated measures may be employed and claimed both in combination as well as singly.

I claim:

1. In a television transmitter a line frequency impulse oscillation generator, a frame frequency impulse oscillation generator, an arrangement for producing a control frequency controlling the first mentioned generator, the second mentioned generator being controlled by the mains frequency, means to conduct the output of said first mentioned generator and the output of said second mentioned generator to a common point of the transmitter, said means comprising screen grid tubes connecting the output of each generator to said point and having a common anode resistby the mains frequency and oscillating at half the 1 chopper and producing a control frequency equal to the double of the line frequency, a tuned am-- plifler for said control frequency, a line frequency impulse generator controlled by said control frequency and a frame frequency impulse generator controlled by the mains frequency and oscillating at the mains frequency, means to conduct the said control frequency additionally to the input of said frame frequency generator so 'as to synchronize it.

SCI-ILESINGER. 

